diff --git a/t/t4205-log-pretty-formats.sh b/t/t4205-log-pretty-formats.sh
index e3905baa3c473b..aac9e4ce6cd510 100755
--- a/t/t4205-log-pretty-formats.sh
+++ b/t/t4205-log-pretty-formats.sh
@@ -922,4 +922,12 @@ test_expect_success EXPENSIVE,SIZE_T_IS_64BIT 'log --pretty with huge commit mes
 	test_cmp expect actual
 '
 
+test_expect_success EXPENSIVE,SIZE_T_IS_64BIT 'log --pretty with huge commit message does not cause allocation failure' '
+	test_must_fail git log -1 --format="%<(1)%B" $huge_commit 2>error &&
+	cat >expect <<-EOF &&
+	fatal: number too large to represent as int on this platform: 2147483649
+	EOF
+	test_cmp expect error
+'
+
 test_done
diff --git a/utf8.c b/utf8.c
index 6a21fd6a7b0253..30c7787cfa9a56 100644
--- a/utf8.c
+++ b/utf8.c
@@ -208,11 +208,12 @@ int utf8_width(const char **start, size_t *remainder_p)
  */
 int utf8_strnwidth(const char *string, size_t len, int skip_ansi)
 {
-	int width = 0;
 	const char *orig = string;
+	size_t width = 0;
 
 	while (string && string < orig + len) {
-		int glyph_width, skip;
+		int glyph_width;
+		size_t skip;
 
 		while (skip_ansi &&
 		       (skip = display_mode_esc_sequence_len(string)) != 0)
@@ -222,7 +223,12 @@ int utf8_strnwidth(const char *string, size_t len, int skip_ansi)
 		if (glyph_width > 0)
 			width += glyph_width;
 	}
-	return string ? width : len;
+
+	/*
+	 * TODO: fix the interface of this function and `utf8_strwidth()` to
+	 * return `size_t` instead of `int`.
+	 */
+	return cast_size_t_to_int(string ? width : len);
 }
 
 int utf8_strwidth(const char *string)